Hydrogeochemical Processes Regulating the Groundwater Geochemistry and Human Health Risk of Groundwater in the Rural Areas of the Wei River Basin, China

The hydrochemical characteristics of phreatic water were evaluated in this study, and the hydrogeochemical processes occurring along groundwater flow paths were analyzed using inverse hydrogeochemical simulations. The spatial distributions of groundwater Fe and Mn contents in the study area, their influencing factors, and their correlative probabilistic human health risks were assessed. The results showed that the order of cation content in phreatic water was Ca2+ > Mg2+ > Na+ > K+ and Ca2+ > Na+ > Mg2+ > K+ in the pluvial-alluvial fan and alluvial plain, respectively. Approximately 92.73% of the phreatic water samples were HCO3-Ca center dot Mg-type water, and only a few belonged to SO4 center dot Cl-Ca center dot Mg-type water. Twelve percent and forty percent of the phreatic water in the pluvial-alluvial fan and alluvial plain, respectively, showed Fe and Mn concentrations exceeding China's drinking water standards. Hydrogeochemical simulations using PHREEQC showed some differences in water-rock interactions between paths and along the same path due to differences in lithological and hydrological conditions. In addition, higher Fe and Mn contents mainly occurred in the Huyi District, as well as in some parts of the alluvial plain aquifer. Moreover, groundwater Fe and Mn contents were mainly influenced by redox potential, infiltration of sewage containing high Fe and Mn concentrations, TDS contents, and groundwater flow rates. In the Wei River basin, the probability of the health risk due to NO3-N, Fe, and Mn was ordered as NO3-N > Mn > Fe. The health risks of NO3-N were 3.1% and 18.3% for adults and children, respectively, and the health risks due to Mn were 2.3% and 4.9% for adults and children, respectively. In contrast, the probability of health risk of Fe was negligible.